A lubricant is a substance capable of reducing friction, heat and wear when introduced as a film between solid surfaces. Efforts to improve upon the performance of mineral oil based lubricants have been the focus of important research and development activities in the petrochemical industry for over 50 years. Maintenance of friction reducing properties, extended useful life in terms of thermal and oxidative stability and wear protection, improved viscosity index and pour point equal to or better than miner oil are performance areas where research and development activities have occurred. (Viscosity index is a number assigned as a measure of the constancy of the viscosity of a lubricating oil with change of temperature with higher numbers indicating viscosities that change little with temperature, and is determined according to ASTM D2270.) These efforts have led to the introduction of a number of synthetic fluids including polyalpha-olefin (PAO) synthetics primarily made by oligomerization of alpha-olefins or 1-alkenes. A synthetic fluid is a term that can describe materials useful as lubricants, heat transfer agents, and corrosion inhibition among other uses. Polyalpha-olefin synthetic fluid compositions are saturated hydrocarbons and thus are less polar than mineral oil based compositions that can contain polar moieties including aromatics. To improve the solvency and dispersancy of poly alpha-olefin (PAO) type fluids a polar co-basestock is added to the composition to help dissolve polar additives of the composition and sludge during usage. A polar co-basestock such as ester or alkylaromatics is typically used in amounts of about 3 to about 50 weight percent of the basestock composition. The polar co-basestock could introduce undesirable side effects such as hydrolytic instability if an ester co-basestock is used or poorer low temperature properties, reduced cleanliness properties if typical alkylaromatic co-basestocks are used. Thus, synthetic fluids are often formulated with additives to enhance their properties for specific applications. Additives that are commonly used can include oxidation inhibitors, dispersants, detergents, rust inhibitors, antiwear agents, extreme pressure agents, metal passivators, pour point depressants, viscosity index (VI) improvers, and the like. Thus formulated fluids are compositions comprising a number of components, the largest volume component being the fluid basestock. Adding to the complexity of formulating lubricating oils is the trend to ever-higher oil performance standards dictated by the increasing complexity of newer equipment and engines. There is a continuing need to improve the suite of properties of the fluid basestock to provide improved performance of the formulated fluid in all areas required including thermal and oxidative stability.
Aromatic hydroxy compounds can be alkylated with polyolefins using acid catalysts for the preparation of polyalkenylphenols. This Friedel-Crafts alkylation does not generally lead to pure monoalkylation products since the alkylated products are more reactive than the unsubstituted starting materials. A mixture of different mono-, di- and polyalkylation products is therefore generally formed. Moreover, when high molecular weight alkylating agents are used, fragmentation reactions frequently occur both in the polyolefin and in the alkylated product, so that as a rule a product mixture having a complex composition is obtained. (For more information on alkylation of Phenols see Shuikin, N. I.; Viktorova, E. A., Russ. Chem. Rev. 29,560 (1960) and U.S. Pat. No. 5,334,775.)
Such mixtures are unsuitable for many industrial applications. Rather, products of defined composition are required, frequently monoalkylation products, it also being possible for the position of the alkylation to be relevant.
Prior to this invention, known processes for the alkylation of hydroxyaromatic compounds with polyolefins have had at least one or more of the following disadvantages: 1) large excesses of hydroxyaromatic compound and/or amounts of catalyst are required, 2) the polyolefin used must contain a high proportion of alpha-olefin terminal units, 3) fragmentation reactions of the polyolefin or of the alkylated product take place, 4) undesirable byproducts, such as polyalkylation products or products alkylated in an undesirable position, are also obtained, and/or 5) the reaction times are long.
PAOs are non-polar and hence it is desirable to increase their polarity via alkylation with polar molecules such as phenols. PAOs produced using metallocene type catalysts have high amounts of terminal vinylidene type double bond or double bonds at more accessible positions. Thus, they are more reactive towards alkylation with hydroxyaromatic compounds like phenols or naphthols.
Therefore, a need exists for polyalkenylhydroxyaromatics and a process to prepare them that address one or more of the aforementioned disadvantages.